Flexible shafts comprise basic elements of power transmission and are designed to transmit power or control from a driving element to an element to be driven. Transmission may be over, under, or around obstacles or objects where transmission by solid shafts would be impractical or impossible.
In a typical rotatable flexible shaft, a wire mandrel has a plurality of layers of closely coiled wire wound thereover, each of the layers being successively wound over another in alternately opposing directions, i.e., right or left-hand lay. This shaft is usually covered by a flexible casing, metallic or covered, and a clearance between the shaft and casing is provided in order that the shaft may rotate freely within the casing.
Rotatable flexible shafts are of two basic types--power driven and remotely controlled. Power driven flexible shafts are designed primarily for motor-driven or high speed operation in one direction. Remote control flexible shafts, on the other hand, are designed primarily for hand-operated control in either direction of rotation.
A power driven flexible shaft has maximum torque capacity when operated in the direction which tightens up its outermost layer of wires. When operated in the opposite direction, torque capacity is reduced by about 20 to 50%. Therefore, for clockwise driving, a left-lay shaft should be used. Alternatively, a right-lay shaft should be employed for counterclockwise driving.
The present invention contemplates a simple, inexpensive drive clutch or torque limiter for use with power driven flexible drive shafts to provide positive fail-safe control. The device is easy to maintain, lends itself to quick coupling, and provides an audible warning of slip condition when the driven member is overloaded.